Corynebacterium, especially Corynebacterium glutamicum, is a Gram-positive microorganism used for the production of L-amino acid. L-amino acid, particularly L-lysine, has been widely used for the production of animal feeds, medicines for human, and cosmetics. This amino acid is generated by the fermentation using Corynebacterium. 
The conventional production method of L-lysine has used Corynebacterium having enhanced L-lysine biosynthesis related gene. For example, U.S. Pat. No. 6,746,855 describes a production method of L-lysine by culturing Corynebacterium sp. which enhanced the lysine releasing carrier gene lysE and introduced with an additional gene selected from the group consisting of dapA encoding dihydrodipicolinate synthase, lysC encoding aspartate kinase, pyc encoding pyruvate carboxylase and dapB encoding dihydropicolinate reductase. And, U.S. Pat. No. 6,221,636 describes Corynebacteria transformed with recombinant DNA containing the DNA sequence encoding diaminopimelate dicarboxylase and the DNA sequence encoding aspartokinase which is substantially insensitive to feedback inhibition by L-lysine and L-threonine.
To enhance the said L-lysine biosynthesis related gene without an antibiotic-resistant sequence, either the number of gene copies is increased or the enzyme activity is increased by mutation. There are two methods reported so far to increase the number of gene copies.
One of the two methods to increase the number of copies is tandem repeat which inserts an additional gene into the right next to the intrinsic gene. The other method is to insert an additional gene into one or more chromosome regions of Corynebacterium sp. (U.S. Pat. No. 7,160,711). However, these methods are limited in gene insertion sites, indicating that it is very difficult to insert multiple genes. To overcome this problem, it has been attempted to insert target genes in the region of multiple copies of rDNA on the genome. It was reported that this method was more successful than the previous ones. Nevertheless, this method has still a limitation because the destruction of two or more rDNA copies can affect the growth of the microorganism.
Transposon is also called Insertional Sequence Element, which is the sequence that can be moved on chromosome or on plasmid. Transposon includes transposase, which shows the activity to recognize a specific sequence for the insertion. Up to date, hundreds of transposons have been reported in a variety of bacteria (TRANSPOSON-BASED STRATEGIES FOR MICROBIAL FUNCTIONAL GENOMICS AND PROTEOMICS (2003) Annual Review of Genetics 37: 3-29 Finbarr Hayes).